In recent years, apparatuses for obtaining information on sheet materials are attracting attention. For instance, U.S. Pat. No. 6,291,829 discloses a device for identifying the type of recording paper sheet provided in an image-forming apparatus.
The sheet materials to be detected include anisotropic materials. U.S. Pat. No. 5,475,233 discloses a method for measuring orientation of fiber in anisotropic materials.
In identification of an anisotropic sheet material with a sheet material information-detecting apparatus by application of an external force, the detection result depends on the relative position of the sensor to the sheet material. Therefore, for detection of information on the sheet material fed successively to an image-forming apparatus, so-called oblique feed of the sheet should be prevented to obtain precise information. This is explained below specifically.
Paper sheets produced from wood pulp as the main source material, for instance, are widely used as recording sheets. The paper sheets have anisotropic characters owing to orientation of the fiber in a specific direction (machine direction) in the paper making process.
Such paper sheets, which are generally cut in machine direction and cross direction, are anisotropic in characteristics according to the sheet cutting directions as called “crosswise orientation” or “lengthwise orientation” based on the cutting ends, and the properties thereof differ depending on the orientation directions: the properties such as rigidity, distortion by force, elongation at break, Young's modulus, swelling and curling by water absorption, light reflectivity, surface roughness, and periodic structure.
The inventors of the present invention have studied on detection of information on sheet materials by application of external force onto sheet materials fed successively to an image-forming apparatus or the like. As the results, the inventors have found newly that, when a paper sheet having the aforementioned orientation comes to be fed with its orientation direction oblique to the sheet feed direction, the information on the sheet material is affected by the anisotropy. Such a problem arises also in coated paper sheets and resin films having orientation caused by the production process.
The present invention provides a sheet material information-detecting apparatus excellent in information detecting accuracy.